Radiolabelling Studies on the Lipid Metabolism in the Marine Brown Alga Dictyopteris membranacea

The lipid metabolism of the marine brown alga D. membranaceawas investigated using 2–¹⁴C]acetate, 1–¹⁴C]myristate,l–^I4C]oleate and l–¹⁴C]arachidonate as precursors.On incubation with 2–¹⁴C]acetate, 18:1 and 16:0 werethe main products formed by de novo synthesis and incorporatedinto polar lipids. With all the exogenous substrates used, DGTAwas strongly labelled and the subsequent rapid turnover of radioactivitysuggested a key role for this lipid in the redistribution ofacyl chains and most likely also in the biosynthesis of theeukaryotic galacto-lipids produced in the absence of PC. Inthe glycolipids a continuous accumulation of radioactivity wasobserved with all the substrates used. The labelling kineticsof molecular species of MGDG suggested the desaturation of 18:1to 18:4 and of 20:4 (n-6) to 20:5 (n–3) acids on thislipid. Both PG and PE were primary acceptors of de novo synthesizedfatty acids and exogenous l–¹⁴C]oleate, but no evidenceexists for a further processing of acyl chains on these lipids.TAG, although strongly labelled with all exogenous l–¹⁴CJacids,was not labelled when 2–¹⁴C]acetate was used as a precursorindicating the flux of endogenous fatty acids to be differentof that of exogenously supplied fatty acids. (Received November 4, 1997; Accepted February 23, 1998)